(1) Field of the Invention
The present invention relates generally to a system and method for controlling a vehicle speed to cruise at a desired speed for a vehicle.
(2) Description of the Background Art
Various types of automatic vehicle speed controlling system and method have been proposed which render the vehicles automatically run at a constant cruise speed without manual operations of accelerator pedals.
In vehicles in which the automatic vehicle speed controlling systems are mounted, e.g., during run on a freeway, a set switch is provided to set the vehicle speed to a desired cruise speed when a driver operates the set switch during run of the vehicle at a vehicle speed at which the vehicle cruises. Then, the controlling system automatically adjusts an opening angle of an engine throttle valve to enable the constant cruise at a constant speed. Since the driver is not needed to depress the accelerator pedal at all times, it is convenient for the driver to run the vehicle.
However, in the controlling system described above, such unfavorable cases described below may often occur. For example, the vehicle does not run at the desired target speed during the cruise run using the automatic vehicle speed controlling system depending on external operating conditions around a control unit in the controlling system, e.g., the actual running speed often becomes lower than the target speed.